This website/program add-on is a powerhouse. ProWritingAid points out a lot of ways to tighten up your work. ​It's well worth its price tag in my opinion. Other helpful options are Hemmingway and Grammerly
bookbrush design fantasy books compilation
Done using BookBrush

Upload your cover pics to BookBrush, they have good promotional image builder options. See above image.
​There are free and paid versions. 

Story prompt card deck
I love the Reckless Deck series for when I need a fresh spark. The diverse card decks work well for art or writing. There are multiple decks for beginners, characters, worlds, and genres. ​Check them out!
Story Engine prompt deck
Story Engine is similar to the Reckless Deck, both story prompt cards full of writing sparks. More the merrier in my opinion. ;)
I really like the look of these plotting books. There's several choices from the shop Plot Your Work on etsy. 
The Emotional Thesaurus and accompanying books are powerhouses for any writer looking to diversify their repertoire. 

Some of these links are affiliate links, meaning I get kickback if you click and buy through this portal; however, I only list things I like and use myself.